Room dimensions and acoustic treatment for a control room

Hello! I'm an amateur recording engineer and professional audio visual technician, originally from New Zealand and currently living in Stockholm, Sweden. I've been asked by a friend to assist with the construction of a studio in an old farmhouse in a small village in the countryside in Piemonte, Italy. I've been doing recording for about eight years, initially at recording school, then in my home studio in New Zealand, as well as in a few different environments - rehearsal spaces, living rooms and just a little bit of work in professional environments. Although I never posted here I read a lot when building my home studio in New Zealand and have a good fundamental understanding of acoustics. I thought it best, however, to come here for advice before construction work gets well underway this time to be sure no mistakes are made. All of the construction work will be done by professionals and my role in the project at this stage is just to offer some advice to my friend regarding the design and layout of the space. Initially I'm just looking for help with the planning of the control room, the live room area will be considered more at a later stage. I don't have a photo but will try to describe the space, it's an old hay loft, on the second floor, with all brick construction and concrete floors. At one end of the room the floor drops down, it's about 700mm lower, and the plan is to build a ceiling over this area to turn it in to a control room, with space for storage of instruments above, open in to the live area. The control room floor shape is almost rectangular, the walls are not exactly parallel. We wish to maximise the internal area so hopefully do not need to reduce the length of the space in order to achieve a suitable room ratio, which brings me to the main point of this post, we have flexibility in the height of the room, by either raising the floor or increasing the distance between the roof above and the internal ceiling of the control room. I have worked out that the average width of the room is 2725mm, and the average depth is 5800mm. These two dimensions don't slot directly into any recommended room ratios I found online so I'm wondering how to proceed. The maximum height of the room will be around 3000mm I expect, though it's actually a little difficult for me to be sure about that at the moment. If I can get a recommendation on what could work well then I could go back to the builders to find out what they think. What would a good ceiling height be in order to get even distibution of room modes? Would it be beneficial to reduce the depth of the room? For acoustic treatment in my previous projects I have always used rigid fibreglass, usually 50kg per cubic meter in density, I successfully turned a small bedroom into a usable mixing space by entirely covering the rear wall to a depth of 400mm. My initial thinking for this space is to do something similar, in addition to thinner panels at all of the first reflection points. Would this approach be a good starting point in a space of this size? thanks!

Hi there "jd td", and welcome! :)

The control room floor shape is almost rectangular, the walls are not exactly parallel.

can you fix that? Any chance you can move one of the walls to get them parallel? Or at least angled correctly, at the proper angle?

width of the room is 2725mm, and the average depth is 5800mm. The maximum height of the room will be around 3000mm

That's not a good ratio at all. In fact, on one really good calculator, it comes up as "worst case scenario calculated".

These two dimensions don't slot directly into any recommended room ratios I found online so I'm wondering how to proceed.

Three dimensions. You need three dimensions to define a room ratio, not just two.

What would a good ceiling height be in order to get even distibution of room modes?

Without changing the length, all you can do is bring the ceiling down, but it's going to be pretty low before it gets usable. At 2.3m, you get a ratio of 1 : 1.18 : 2.52, which is reasonable, but not fantastic. But any lower than that and the height starts to be an issue. On the other hand, if you make it shorter then you have far more options. Once you get the length below about 4.5m, you can take the height up to 3.1 m or even higher, and you start getting into some of the good Louden ratios. At 4.2 long and 3.1 high, you get 1 : 1.14 : 1.54, which is pretty good. Very close to Louden's 5th best ratio.

For acoustic treatment in my previous projects I have always used rigid fibreglass, usually 50kg per cubic meter in density,

For fiberglass, the optimum density for MSM isolation is more like 30 kg/m3. The density you mention, 50 kg/m3, is correct for mineral wool, but not too dense for fiberglass. It won' handle low frequencies as well as the less dense stuff.

My initial thinking for this space is to do something similar, in addition to thinner panels at all of the first reflection points. Would this approach be a good starting point in a space of this size?

yes, but the panels cannot be thinner. However, before you start thinking about how to treat the room, you should decide on the design philosophy that you intend to follow, and also figure out the amount of isolation that you will need (in decibels). Those are the basics for getting started on the design. - Stuart -

Soundman2020 wrote:

Hi there "jd td", and welcome! :)

The control room floor shape is almost rectangular, the walls are not exactly parallel.

can you fix that? Any chance you can move one of the walls to get them parallel? Or at least angled correctly, at the proper angle?

Hey, thanks very much for your reply! Indeed it would be possible to get the walls parallel, though as the angle is rather slight it seems like the shape could actually be beneficial for spreading out the standing waves over a slightly wider frequency range The owner of the studio did a little research also, here's what he's sent me: I've done some research here: http://www.bobgolds.com/Mode/RoomModes.htm and found out: if we leave the room length and width as they are and use a 3.0 m roof, its a worst case scenario. By raising the roof to 3.1 m, without changing the length we're at loudens 6th best ratio. By changing the lenght to 4.2, we have loudens 5th best. It seems to me that channging it ain't that important after all as long as we have the roof 3.1 instead of 3.0. As we probably will need to go down a bit on length to add accoustic panels etc, I have found out the furthest amount we can go down before it becomes a worst case scenario again, which is 5.69 m. That gives us only 11 mm of space for panels etc before the room becomes "bad". Furthermore: We can keep raising the roof, and it stays Loudens 6th best for a while, and then become BETTER. If we take it down to 3 m, it becomes worst case, but from 4m and upwards, it becomes Loudens 3d best. NOW BAD HUH? However, I expect that this is all a bit uncertain, gvien that these ratios are for rectangular rooms, this one is not. So it's perhaps better, perhaps worse?

though as the angle is rather slight it seems like the shape could actually be beneficial for spreading out the standing waves over a slightly wider frequency range

Unfortunately, it doesn't really work like that. Modes are very tightly tuned frequencies, with a very high Q, and angling walls does not change that: The Q remains high, and the mode is not "spread out". All that happens is that it moves to a different frequency, but still remains high tuned. It's a common misconception that angling walls "eliminates" all the modes, or "reduces" them: All it does is move them to other frequencies. They are still there, just at different places on the spectrum. If the angles are slight, like yours seem to be, then you can still use calculators (such as Bob Golds' and others) on the average room dimensions to get an idea of the modal response. The greater the angle, the less accurate it becomes, and once you get past splays of a few degrees then it is no longer much use, and you need to resort to other methods to predict room response, such as FEA/FEM.

I have found out the furthest amount we can go down before it becomes a worst case scenario again, which is 5.69 m. That gives us only 11 mm of space for panels etc before the room becomes "bad".

Well, not really. That's the trouble with pure numeric predictions based on a discreet set of possible outcomes. There has to be a single point where the calculator flips over from "good" to "bad" by just varying one dimension by a very tiny amount. Reality is a bit more complex. If we have two identical rooms, one with a length of 5.69 and the other with a length of 5.68, they will sound exactly the same, for all practical purpose. The 5.68 version will not be "terrible" while the 5.69 is "fantastic". Acoustics simply does not work like that. Rather, there will be a gradual change across a wide range of dimensions, from "pretty good" to "not so good". There is no point at which things suddenly jump from "good" to "bad". The only reason why its seems that way from Bob's calculator is because there is only a small number of ratios on the list. So at some point the calculation "jumps" from one to the next. That's why it is better to look at X-Y plots of all possible ratios, showing the good areas and the mediocre areas and the bad areas, and adjust your dimensions more "intelligently", seeing what is happening with each change, until you get to a good compromise.

Furthermore: We can keep raising the roof, and it stays Loudens 6th best for a while, and then become BETTER. If we take it down to 3 m, it becomes worst case, but from 4m and upwards, it becomes Loudens 3d best.

Exactly! It looks like the results are jumping with small changes, but in reality the acoustics are changing only slightly. Besides, it is not just the ratio that matters: It is also the spread of modes. If you look at the bottom of Bob Golds' calculation page, you will see the Bonello chart. That gives you a slightly better idea about how smooth your modal distribution is. You can actually get a "good" ratio, based just on numbers, but when you look at the Bonello chart, it doesn't look so good any more... :) And finally, ratios are not magical: some people spend hours, or even days, trying to tweak their ratios down to the last mm, to get a "perfect" ratio: that's just a total wast of time, since there is no such thing. Ratios are just ONE aspect of studio design, and there are many other aspects that are far more important than that: Room symmetry, for example, is critical. Correct geometry of the speakers and listening position within the room is also important. The shape of the room can be important. The total floor area, and the total room volume are also important aspects. So are construction materials, the building itself, and perhaps more than anything else, the acoustic treatment. Getting a good ratio is important, but even the best ratio cannot compensate for a bad shape, lack of symmetry, poor geometry, or incorrect treatment. All of them have to be worked out together. That's why it takes so long to design a studio properly: there are so many compromises that the designer needs to consider, to figure out what makes the most sense, what combination of these things will give the best possible studio within the available space, and the available budget. So I would suggest that you should just choose a set of dimensions that gets you close to a good ratio, then carry on from there with the next steps in the process, and maybe come back to adjusting that ratio later, each time you come across other aspects of the design that make it necessary. - Stuart -

excellent information, thanks very much for that! we need to do a bit more planning and research then perhaps come back with some more questions